In general, roofs of vehicles comprise a roof panel formed of a thin plate and fixed to a framework. An example vehicular roof structure is know from JP 2005-153649 A and schematically illustrated in FIG. 13 hereof.
In FIG. 13, a roof structure 201 has a hole 204 for insertion therein an electrode for spot-welding a center roof rail 203 to a side roof rail 202 and a hole 206 for insertion therein an electrode for spot-welding a roof panel 205 to the side roof rail 202. With the center roof rail 203 of a closed sectional shape spot-welded to the side roof rail 202, the roof structure 201 can increase mechanical strength of a vehicle body against lateral collision. However, the disclosed roof structure 201 can not achieve a desired increased mechanical strength due to the provision of the electrode-inserting holes 204 and 206.